Field of the Invention
The invention relates to a process and a dispersion apparatus for the production of a powder cloud that is produced when a powder/air mixture emerges from a powder spraying apparatus.
The dispersion apparatus is particularly suitable for spraying apparatuses in which the powder/air mixture emerges from a fluidization chamber through a nozzle. However, it can also be used in other systems, such as a spraying apparatus in which the dispersion apparatus is fed a powder/air mixture through a hose.
In German Published, Non-Prosecuted Patent Application DE 195 37 089 A1, corresponding to U.S. application Ser. No. 08/726,815, filed Oct. 7, 1996, a powder spraying apparatus is described which has a fluidization chamber from which fluidized powder is withdrawn from a fluidized bed with the aid of a withdrawal pipe and passes to the outside through a nozzle. High-voltage electrodes which are disposed in the region of the outlet effect charging of the emerging powder particles.
In the above-mentioned patent application, a configuration of a baffle on which the powder/air mixture emerging from the nozzle impinges and through which a defined powder cloud is developed, is proposed as a dispersion system. However, with that small baffle only specific, relatively small spray clouds may be developed, which are not sufficiently large for some applications. In addition, powder depositions on the baffle may occur in such a configuration. The use of larger baffles in order to produce a large cloud is therefore ruled out because of the more severe powder deposition on the baffle that occurs in this case.
In order to generate a relatively broad powder cloud while avoiding powder deposits, Published European Patent Application 0 574 305 A1 proposes a dispersion system having a rapidly rotating disc, wherein rotational speeds of over 3000 rev/min are used. However, such systems are mechanically sensitive and have only a limited lifetime in powder spraying apparatuses.
U.S. Pat. No. 3,659,151 and U.S. Pat. No. 3,740,612 describe dispersion systems that operate with additional air that is introduced tangentially in order to produce a powder cloud. In these systems, however, use is also made of central baffles, on which powder may be deposited. The geometry of the configurations is not suitable for spraying powder/air mixtures with a high powder loading, nor for producing large spray clouds.